Automatic Defect Classification (ADC) techniques are widely used in inspection and measurement of defects on patterned wafers in the semiconductor industry. The object of these techniques is not only to detect the existence of defects, but to classify them automatically by type, in order to provide more detailed feedback on the production process and reduce the load on human inspectors. ADC is used, for example, to distinguish among types of defects arising from particulate contaminants on the wafer surface and defects associated with irregularities in the microcircuit pattern itself, and may also identify specific types of particles and irregularities.
Various methods for ADC have been described in the patent literature. For example, U.S. Pat. No. 6,256,093 describes a system for on-the-fly ADC in a scanned wafer. A light source illuminates the scanned wafer so as to generate an illuminating spot on the wafer. Light scattered from the spot is sensed by at least two spaced-apart detectors, and is analyzed so as to detect defects in the wafer and classify the defects into distinct defect types.
As another example, U.S. Pat. No. 6,922,482 describes a method and apparatus for automatically classifying a defect on the surface of a semiconductor wafer into one of a number of core classes, using a core classifier employing boundary and topographical information. The defect is then further classified into a subclass using a specific adaptive classifier that is associated with the core class and trained to classify defects from only a limited number of related core classes. Defects that cannot be classified by the core classifier or the specific adaptive classifiers are classified by a full classifier.